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Theories Evolve in T. Rex Discoveries

A graduate student raps with a hammer and chisel at a dinosaur bone encased in yellow rock, out of rhythm with the Carole King song playing here in John R. Horner's paleontology laboratory at the Museum of the Rockies.

Dr. Horner and his wife, Celeste, are back in his crammed office off to the side of the laboratory, after returning from the digs in Eastern Montana, where research teams had spent a third summer studying ecosystem evolution at the end of dinosaurs' reign and where they have found five Tyrannosaurus rex skeletons. They will return next summer to excavate the skeletons.

The bones were discovered in the broken, spare landscape of Garfield County, once a seabed and later covered by forests of sequoias, where T. rexes roamed 65 million to 67 million years ago.

Before the find, only 16 other T. rex skeletons had been discovered since Barnum Brown of the American Museum of Natural History in New York uncovered the first one, also in Garfield County, in 1902.

The project has two more years to collect fossils and other clues of evolution in the era of the Tyrannosaurus rex, including climate variations across three million years, which could be useful as a comparison with recent climate changes. The findings may also shed light on why dinosaurs disappeared 65 million years ago.

Dr. Horner, the author of five books on dinosaurs, became known for his research showing how some dinosaurs cared for their young. He was a consultant for the ''Jurassic Park'' movies. His attention is now focused on Tyrannosaurus rex, and he will be studying the skeletons as they come out of the ground next summer. The find includes several early specimens that may be useful in trying to prove his theory that the dinosaur was more scavenger than hunter.

If the arms of the early specimens are longer than those of later ones, it will suggest that the appendages were evolving away, he said. Many predators, like cats, rely on their arms to hold prey, but arms are less essential to scavengers, he argues.

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Dr. Horner describes the Tyrannosaurus rexes feeding like vultures and hyenas do in Africa today.

''All you have to do,'' he said, ''is be big and ugly and mean-looking and stinky to run stuff off.''

Dr. Horner's finds are ''obviously very significant,'' said Dr. Philip J. Currie, an expert on carnivorous dinosaurs and a curator at one of the world's largest dinosaur museums, the Royal Tyrrell Museum of Paleontology in Drumheller, Alberta. ''A T. rex is a rare enough dinosaur that any new find is exciting and newsworthy.''

One of the new specimens appears to be the biggest ever, Dr. Horner said.

It is named Celeste after Dr. Horner's wife, who first spotted its well-preserved pelvis jutting from a bank. While the new specimens await excavation, Dr. Horner said extrapolations of initial measurements suggest that the Celeste skeleton is 10 percent bigger than that of Sue, the nearly complete Tyrannosaurus rex found in South Dakota in August 1990. Sue was sold in 1997 for nearly $8.4 million to the Field Museum of Natural History in Chicago.

How much of Celeste remains is unknown, Dr. Horner said. But, he said, the pelvis, nine articulated vertebrae and a handful of ribs are exposed, suggesting that at least 30 percent of the skeleton is there.

Celeste may be given to the Smithsonian Institution in Washington, he said, though the future of the other skeletons has not been decided. One may end up near where it was found: at the tiny Garfield County Museum, where a weathered sign outside the town of Jordan says, ''T. Rex Capital of the World.''

The Museum of the Rockies will probably get another, Dr. Horner said.

Although the dinosaurs are federal property, Dr. Horner is the arbiter of their future, according to his agreement with the United States Fish and Wildlife Service and the federal Bureau of Land Management.